1. Field of the Invention
This invention relates to a chip-scale infrared emitter package, more particularly to a chip-scale infrared emitter package including a membrane that is provided with an electric resistor and that is suspended in a cavity by a slim supporting beam for efficiently supplying infrared radiation.
2. Description of the Related Art
It is known that incandescent light-emitting sources can be used for generating infrared radiation for non-dispersive infrared (NDIR) gas detection. Conventional incandescent light-emitting sources include filament light bulbs and chip-type infrared emitter sources. The filament light bulbs have disadvantages, such as slow thermal response and high power consumption (about 0.6 Watt), and thus are unsuitable for battery-operated NDIR gas detection.
U.S. Pat. No. 7,989,821 illustrates a method of using semiconductor processing technology to make a sealed infrared emitter source. The infrared emitter source thus formed includes a silicon substrate having a central cavity, an emitter membrane provided with an electrical conductor of polysilicon, and a housing enclosing the silicon substrate and the emitter membrane. The emitter membrane has a peripheral end portion formed on a top surface of the silicon substrate so as to be suspended on the silicon substrate. The housing defines an enclosed space that can be filled with an inert gas or vacuum to avoid oxidation.
U.S. Patent Application Publication No. 2012/0267532 discloses an infrared emitter source that includes a silicon substrate having a central cavity, a membrane suspended on the silicon substrate, and a resistive heater formed on the membrane. Similar to the aforesaid U.S. patent, the membrane has a peripheral end portion that is formed on a top surface of the silicon substrate.
Although the sizes of the infrared emitter sources of the aforementioned U.S. patent and the U.S. patent application publication can be miniaturized, none of the aforementioned U.S. patent and the U.S. patent application publication teaches forming a loop-shaped gap between a peripheral end of the membrane and a periphery of the central cavity of the silicon substrate for thermally isolating the membrane from the silicon substrate for reducing heat loss of the membrane. In addition, none of the aforementioned U.S. patent and the U.S. patent application publication teaches that the pressure in the central cavity has a critical effect on the electro-optical efficiency (i.e., the efficiency of converting electrical power into light energy) of the infrared radiation source.